Predictive control of a series-input, parallel-output, back-to-back, flying-capacitor multilevel converter

[摘要] ENGLISH ABSTRACT: This thesis investigates the viability of constructing a solid-state transformer (SST) witha series-input, parallel-output connection of full-bridge, three-level ying-capacitor converters.It focusses on the active recti er front-end of the SST which is used to controlthe input current to be sinusoidal and in-phase with the sinusoidal input voltage. A stackof two converters are built and tested. The input current, as well as the ying capacitorvoltages of the two active recti ers in the stack, are actively controlled by anite-statemodel-based predictive (FS-MPC) controller.The use of multiple ying-capacitor converters poses a problem when using FS-MPCbecause of the large number of possible switching states to include in the predictionequations. Three FS-MPC control algorithms are proposed to attempt to overcome theproblem associated with the large number of switching states. They are implementedon an FPGA digital controller. The algorithms are compared on the bases of voltageand current errors, as well as their responses to disturbances that are introduced intothe system. The simulation and experimental results that are presented shows that byinterleaving the control actions for the two converters, one can obtain fast and robustresponses of the controlled variables. The viability of extending the interleaving controlalgorithm beyond two converters is also motivated.

[发布机构] Stellenbosch University